Genomic and exoproteomic diversity in plant biomass degradation approaches among Aspergilli

Abstract

We classified the genes encoding carbohydrate-active enzymes (CAZymes) in 17 sequenced genomes representing 16 evolutionarily diverse Aspergillus species. We performed a phylogenetic analysis of the encoding enzymes, along with experimentally characterized CAZymes, to assign molecular function to the Aspergilli CAZyme families and subfamilies. Genome content analysis revealed that the numbers of CAZy genes per CAZy family related to plant biomass degradation follow closely the taxonomic distance between the species. On the other hand, growth analysis showed almost no correlation between the number of CAZyme genes and the efficiency in polysaccharide utilization. The exception is A. clavatus where a reduced number of pectinolytic enzymes can be correlated with poor growth on pectin. To gain detailed information on the enzymes used by Aspergilli to breakdown complex biomass, we conducted exoproteome analysis by mass spectrometry. These results showed that Aspergilli produce many different enzymes mixtures in the presence of sugar beet pulp and wheat bran. Despite the diverse enzyme mixtures produced, species of section Nigri, A. aculeatus, A. nidulans and A. terreus, produce mixtures of enzymes with activities that are capable of digesting all the major polysaccharides in the available substrates, suggesting that they are capable of degrading all the polysaccharides present simultaneously. For the other Aspergilli, typically the enzymes produced are targeted to a subset of polysaccharides present, suggesting that they can digest only a subset of polysaccharides at a given time.